1. Field of the Invention
The present invention relates to modified polymer hydrogels specially adapted for use as soft contact lenses. More specifically, this invention relates to covalent modification of the polymer hydrogel forming the contact lens surface or matrix with a surfactant in order to prevent or substantially reduce the formation of calcium, lipid and protein deposits on the lens when worn on the human eye.
2. Description of Related Art
The rapid formation of calcium, lipid and protein deposits on human worn soft contact lenses is one of the most severe problems associated with the use of these lenses. The removal of such deposits with cleaning agents is not always possible, and in some cases may create additional problems. Accordingly, the development of soft contact lenses which are resistant to the formation of such deposits has been greatly desired.
Copolymers based on acrylic esters may be utilized to form the so called polymeric hydrogels which are widely in use as soft contact lenses. These copolymers contain polar functional groups and have a matrix which is able to bind a high percentage of water and a variety of chemicals.
The known methods of modifying soft contact lenses with chemicals to prevent the formation of calcium, lipid or protein deposits are based on molecular absorption principles. These methods may be summarized as follows:
A. Soft contact lenses which are dipped into aqueous solutions of polyamines or polyquats tend to absorb these molecules, whereby the lenses may become positively charged. As a result of this modification, the lenses repel calcium ions and consequently are resistant to the formation of calcium deposits.
B. Soft contact lenses which are dipped into aqueous solutions of surfactants develop characteristics which prevent lipid and protein deposits.
In the above-identified methods, the chemical agents are sorbed at least at the lens surface by electrostatic interaction or van der Waals' forces. The antideposit activity is lost when the modified lenses are washed with cleaning agents or rinsed thoroughly with physiological salt solution, i.e., the activity for the prevention of calcium, lipid or protein deposits disappears as a function of the order of magnitude of the migration and separation of the chemical agents from the lens surface.
It is known that incubation of soft contact lenses with polyamines or aminoalcohols in aqueous solutions at elevated temperatures results in covalent linkage of the amine through an interchange reaction of the acrylic ester residues of the lens matrix, forming covalent C--N bonds in the polymer structures; see in this regard U.S. Pat. Nos. 4,097,657 and 4,128,318. In this case, molecular migration or separation of the chemical agent cannot take place, and the modified soft contact lenses are reported to be resistant to substances which cause lens clouding.